It is generally known that petroleum consist of a complex mixture of many hydrocarbons, including the so-called polynuclear aromatics (PNAs). These PNAs, being relatively high boiling, are substantially absent in distillation cuts boiling below 500.degree. F., but are found in higher boiling fractions in increasing concentration as the boiling point increases, and in the residuum. Materials classed as PNAs have from three to seven or more condensed rings, some of which may be partially saturated, and they usually have one or more alkyl and/or cycloalkyl side chains of various molecular weights. In addition, some of the PNAs contain sulfur as a heteroatom, and may only be separated from the pure hydrocarbon PNAs with great difficulty, if at all. It is also known that the content of PNAs, and probably the distribution of their molecular weights, vary with the petroleum source. See "Encyclopedia of Chemical Technology", Kirk-Othmer, 3rd Edition, Petroleum Composition, Vol. 17, pp 119-129, incorporated herein by reference as background material.
PNAs are of importance for at least two reasons. In petroleum refining, they may adversely affect the practical properties of certain lubricants and other products. In such instances, they usually are removed or converted to other hydrocarbons types. And, ecologically, some of the PNAs are recognized to have dermal carcinogenic activity.
The generally accepted method for evaluating the carcinogenic activity of petroleum products involves animal tests in which animals such as mice are exposed to the hydrocarbon by painting a portion of the skin repeatedly over a long period of time, and evaluating the tendency of such exposure to produce malignant growths. It is generally recognized that this test method requires seventy to eighty weeks of exposure to produce reliable results, and therefore that the method is not suited for situations in which a quick indication of potential carcinogenic activity is required.
In vitro mutagenic activity assays, such as, for example, the Salmonella Microsomal Activation Assay described by B. N. Ames, J. McCann, and E. Yamasaki in Mutat. Research, 31, 347-364 (1975), hereinafter referred to as the "Ames test", provide a rapid, inexpensive method for screening chemicals for carcinogenic potential. The entire content of this publication is incorporated herein by reference as if fully set forth. In general, the predictability of this assay with simple chemicals is good; validation studies have produced a 65-90% correlation between mutagenic activity and carcinogenic activity for many relatively pure compounds. However, the assay is unsuited to the testing of water insoluble complex mixtures, such as the complex hydrocarbon mixtures encountered in petroleum refinery streams. Attempts to use the Ames test procedure with such materials give results which are not reproducible and do not relate in a significant way to the known carcinogenic activity for previously tested mixtures.
Blackburn et al. U.S. Pat. No. 4,499,187 discloses a modification of the Ames test, hereinafter referred to as the "Modified Ames Test" suitable for use with complex hydrocarbon mixtures. The modification, in essence, involves the preparation of a DMSO (dimethylsulfoxide) extract of the sample being evaluated, and use of the DMSO extract instead of the sample itself in the Ames test together with an optimal amount of metabolic activator such as induced rat liver homogenate S-9. Detailed descriptions of the method for preparing the extract and for the assay itself are given in U.S. Pat. No. 4,499,187, the entire content of which is incorporated herein by reference. The Modified Ames Test, unlike the Ames test itself, provides a rapid and reproducible measure of the mutagenic activity of petroleum hydrocarbon mixtures, and the results of such assays strongly correlate with the carcinogenic activity index found for the mixtures by skin painting.
The Modified Ames Test described above is much more rapid than skin painting, requiring only about two to three days to complete an assay compared with 18 months. There remains a need, however, for a less labor-intensive and less costly assay.
It is an object of this invention to provide a rapid, inexpensive and very sensitive chemical method for assaying the PNA content of a hydrocarbon oil. It is a further object to provide a rapid chemical method for assaying the mutagenicity and potential carcinogenic potency of a hydrocarbon oil derived from petroleum. It is a still further object of this invention to provide a rapid method for controlling certain petroleum refinery processes wherein PNAs are segregated, such as solvent extraction. These and other objects will become evident to one skilled in the art on reading this entire specification, including the appended claims.